I know that you can keep other fish with a mated pair but I leave that to the experts to answer. I know that my friend Lisa keeps a mated pair in her tank along with a shoal of Dennison barbs, and a herd of loaches. At the moment I don't recall the other fish in her tank. Her tank is a 125gl, six feet long!
I would think that Congo or Columbian tetras would do well as they are too fast for Angels to get near. Since Lisa's loaches aren't bothered by her mated pair I would think any "bottom" dwelling fish would fare well with Angels. I would think that there would be many fish that would be fine in a tank with a mated pair of Angels, just not sure how the mated pair would feel about those fish, though.
Discus aren't Angels, but to illustrate, my mated pairs of Discus were extremely disturbed by the fast swimming behaviors of my Congos and Dennisons so these barbs and tetras were moved to a tank of their own.